Manufacture of krypton and xenon



1955 M. P. HNILICKA 2,698,523

MANUFACTURE OF KRYPTON AND XENON Filed April 28, 1950 2 Sheets-Sheet 1 4.4.5 97 flDJURBE/YS I N VEN TOR.

Jan. 4, 1955 M. P. HNILICKA 2,693,523

MANUFACTURE OF KRYPTON AND XENON Filed April 28, 1950 2 Sheets-Sheet 2 ABSORBER-5 15 L/[IUI HITSUKBER .9 f7 TTOR/VE) United States Patent Ofifice 2,698,523 Patented Jan. 4, {9055 MAWUFACTURE OF KRYPTON AND XENON Miloslav P. Hnilicka, Brownsville, Tex., assignor to Carthage Hydrocol, Inc., New York, N. Y., a corporation of Delaware Application April 28, 1950, Serial No. 158,639

20 Claims. (Cl. 62123) This invention relates to the recovery of krypton and xenon from air, and particularly, is directed to a process and apparatus for obtaining krypton and xenon from air as a by-product during the recovery of oxygen.

During the development of the electric light bulb, it was found that the candle power could be increased and the life of the tungsten filament prolonged by the use or inert gases with high atomic weights. Specifically, it was discovered that nitrogen, and later argon, were particularly valuable. Further research and development in the electric bulb industry has proved that the rare gas krypton having an atomic Weight of 83.70 would bring even greater improvement. However, there have been no successful means of producing krypton in sufficient quantity or economically for Wide-scale use, for krypton is present in air in the extreme dilution of 0.9 part per million by volume.

The potential market for krypton, if used for incandescent bulbs at the present rate of manufacture, can be very conservatively estimated at between 1,000 and 2,000 S. C. F. D. of krypton. v

Another market for krypton is the fluorescent lamp; however, the present small production and high price of this rare gas makes it unavailable.

Xenon is a rare and inert gas with a higher boiling point than krypton of l60.8 F. at atmospheric pressure. lt is present in atmospheric air in extreme dilution of 0.09 part per million by volume. It is distinguished by very favorable discharge light spectrum similar to the daylight. At the present time, special electric discharge lamps with xenon are used as an intensive flash light source in photography and high intensity lighting purposes of runways at airports. The brightness of these flash lamps exceeds many times that of the sun. At the present time, available supply of xenon is even more restricted and market prices higher than those of krypton, because production of xenon requires processing and liquefaction of extremely large volumes of air.

The recovery of krypton and xenon from atmospheric gases. or liquefied gases by low temperature adsorption has been known, but no effective means of recovery of the desorbed gases has been evolved. Adsorption materials such as silica gel or charcoal have been used in the adsorption of krypton and this method has been used for laboratory practice and small scale operations. However, it must be borne in mind that the major difficulty of industrial recovery of krypton and xenon is the danger of acetylene explosion, because simultaneously with the adsorption of krypton, and xenon, hydrocarbons, including acetylene, are also adsorbed by silica gel from the air and upon desorption are subsequently recovered together with the rare gases.

in the past, due to the small quantities which were being handled in laboratory practice, this fact was of little importance, but for the large scale operations the success of the krypton and xenon recovery is dependent upon an effective means for eliminating the acetylene as an impurity in krypton and xenon and as an explosion hazard during the recovery process.

It is an important object of this invention to provide a method and apparatus for efl ectively and economically recovering krypton from air and removing the hydrocarhon impurities which are adsorbed with the krypton and xenon during the process.

A further object of the invention is to provide a method and apparatus for recovering krypton and xenon which may be used in conjunction with an oxygen recovery system and which effectively disposes of the hydro carbon impurities and the explosion hazard incident to their presence in such a system. A still further object of the invention is to provide a practical means or recovering krypton and xenon in relatively pure form.

The process and apparatus of this invention will be described with reference to the drawings, wherein:

Fig. l is a diagrammatic arrangement of the krypton and xenon recovery apparatus of this invention, illustrating the first phase of the recovery;

Fig. 2 is a diagrammatic arrangement of the portion of the apparatus shown in Fig. 1, taken along the line 2-2, indicating the second phase of the recovery;

Fig. 3 is a diagrammatic arrangement of a portion of the krypton and xenon recovery apparatus according to this invention illustrating another location of adsorbers during the first phase of recovery by adsorption in a conventional oxygen plant; and

Fig. 4 is a diagrammatic alternative arrangement of the desorption part of the apparatus.

Figs. 1 and 2, which schematically represent the salient features of a process for producing oxygen from air, include a heat exchanger 10, a high pressure air fractionator 11 and a low pressure oxygen fractionator 12. To this oxygen recovery apparatus is added the krypton and xenon recovery apparatus which includes a pair of gas adsorbers 13 and 14 and or a pair of liquid adsorbers 15 and 16. Each pair of adsorbers is so arranged with switch valves that they may be used alternatively with one adsorber, oil-stream, actively adsorbing, and the other off-stream and desorbing. The active adsorber 13 of the first pair is preferably maintained at -272 F. and the active adsorber 15 of the second pair is preferably maintained at 252 F. Also included in the apparatus are two condensing coils 17 and 18.

During the first phase of the krypton and xenon recovery, as shown in Fig. 1, the condensing coil 17, for condensing acetylene, is preferably operated at F. and the condensing coil 18 for condensing krypton and xenon is preferably operated at 289 F. An auxiliary refrigeration system 19 employing a suitable refrigerant as, for example, ethylene is used to maintain the condensing coil 17 at l50 F. and liquid oxygen 56 from the bottom of the low pressure oxygen fractionator 12 is utilized foggmagitaining the condenser 18 at approximately 0 The first phase of the krypton and xenon recovery process comprises introducing a stream of compressed air at 75 lbs. pressure into the system through feed line 20. The atmospheric air contains the usual constituents such as nitrogen, oxygen, rare gases, including krypton and xenon, and also contains certain hydrocarbon impurities including acetylene. The air passes into the heat exchanger 10, which is typical of any recuperative or regenerative exchanger system, wherein it is cooled by the cold nitrogen and oxygen passing, respectively through lines 21 and 22, the nitrogen and oxygen having a temperature of approximately 300 F. at the time they enter the heat exchanger.

After being cooled, the air stream, from which moisture and carbon dioxide have been largely removed, issues from the heat exchanger 10 through line 23, flows into the gas adsorbing chamber 13, which as illustrated in Fig. 1 is the gas adsorbing chamber which is on-stream. The air flows through a bed of silica gel or other suitable adsorbing material contained in the adsorbing chamber 13. The temperature of the air as it fiows through the bed is about -272 F. and krypton, xenon, and acetylene which are in the cold air stream are adsorbed over a period of time, until the silica gel is largely saturated, whereupon the switch valves 24 and 25 are turned to divert the stream through the alternate gas adsorber 14.

After the cold air has passed from the adsorber 13 and is largely free from the acetylene, krypton, and xenon previously contained therein, it continues in the usual way, part of it constituting a high pressure air feed passing through line 26 to the high pressure air fractionator 11 and another part passing through line 27 to expander 28 and entering the low pressure oxygen fractionator 12 at 29.

In the high pressure air fractionator 11 the liquid oxygen bottoms 55 are drawn off through line 39 and pass into liquid adsorber 15, or alternately 16, which are thus maintained at 275 F. and any acetylene, xenon, and krypton which are present in the liquid stream are therein adsorbed and the; purified product is passed into thelow pressure oxygen fractionator '12 through line 31.

An alternative arrangement for adsorption of krypton and xenon in a conventional oxygen plant is represented in Fig. 3; wherein the adso'rbers 61l and 61 are located in the exhaustline from expander 98 thereby taking advantage of better adsorption at lower temperatures. The exhaust from the expander vat 'a temperature approximately 300 F; improves the ratio of partial pressure of krypton and xenon to correspondingly saturation pressures of said gases to those of common air components which is theoretically desirable for better adsorption.

Liquid adsorbers' '6 2 an d Glare located in the oxygen drain line from main reb In such an arrangement, krypton and xenon are considerably concentrated because in reboiler 113 a major part of the liquid oxygen is evaporated as reboil, necessary for the low pressure tower fractionation.

Krypton and xenon 'dissolvedjin oxygen and having relatively high' boiling points remained in the bottoms of reboiler 113. The adsorption of these gases at a higher concentrationfrom liquid oxygen is more effective and the size of equipment may be considerably smaller. I

For a more complete description of the alternative arrangement of the adsorbers, reference is made to Fig. 3. The air stream at 75 lbs. pressure is introduced through line 9%). The moisture and carbon dioxide have been previously removed by cooling to liquefaction temperature by heat exchange with oxygen products and nitrogen vents, carried respectively in lines 92 and 91. The

air stream issuesfr om heat exchanger 84) through line $3 part going directly to high pressure tower 81, through line 96, and part going through line 97 to expander turbine 98. By the expansion in turbine 98 from 75 lbs. to atmospheric pressure, the air is cooled to approximately 3()0 F; and flows through reversing valve 94 to the gas adsorbing chamber '61 which, as illustrated in Fig. '3, is the adsorb'er in the stream. in this. arrangement; thete'mperatureof the air as it enters the ad sorber61 andflows through the bed ofsilica :gel or other a suitable adsorbent "material at nearly atmospheric pressure isj '3 'F Krypton, xenon and acetylene con tained -in this stream are 'cdoled far below their boiling points. Consequently, silica gel or other convenient adsorbent, cooled to 300 F. y/ill adsorb from the air stream, krypton, xenon and acetylene over a period drains untilfthe silica gel is largely saturated,

whereupon-the switch valves "94 and 95 are turned to divertljth'e stream of air through standby gas adsorber 6i). 'lhe efilue'nt from the adsorber is largely free of rare 'g'ses and acetylene and continues its flow in the usuai way through the line 99 to 'enter low pressure oxygen '-fractionator 82.

Krypton, xenon, and ates/ten; mamma s the other part of the process air are liquified in the high pressure tower 81 andare dissolve'din liquid oxygen in the bottom of low pressure tower 82, In reboilers 113, the major part of the liquid is evaporated to furnish reboil for .final fractionationin tower 82. Krypton, xenon and acetylene are thus concentrated because of considerably higher boiling points and are drawn oil from the reboilers through line '6 4. These oxygen bottoms enriched in krypton, xenon and acetylene enter the liquid adsorber 62 or alternately 63 at a temperature of approximately 288? F. Acetylene, kryton and xenon present in this stream in a higher concentration than originally in the liquified atmospheric'air in the line 1% from the high pressure tower 31 are, therein adsorbed by silica gel or other adsorbent. Purified liquid oxygen, from which hazardous acetylene was removed, enters through line 67, the product of evaporator 59, in which it is completely evaporated. Gaseous oxygen from product evaporator 59 issues through line '71 to the line 92 and enters heat exchanger 8% Where it is warmed up by heat exchange withjneorhing-process air to atmospheric temperature. Liquid adsorbers 62, '63 are provided with reversing valves 65 and6 6 enablingswitching of the liquid air stream when adsorbing capacity ot theadsorber on-stream is exhaustedto astandby adsorber and vice versa. i

orlers 113'to product evaporators Fig'. 3 may be substituted for the adsorbing circuit his recovery system shown in Fig. l, and thus combined, may be utilized as an integral part of a krypton and xenon recovery system.

The relative quantity of adsorbed gases in an adsorbent at a given temperature depends upon the molecular structure and the ratio of partial pressures and corresponding saturation pressure of the vapors of the concerned gases at the same temperature. Because the boiling points of argon, -302 R, oxygen, -297.4 I F., nitrogen, -320 F., are considerablylower {than those of krypton, -252 F., and xenon, l60.6 F.,'the saturated vapor pressures at the adsorption temperature of argon, oxygen and nitrogen will bemany times higher than those of krypton and xenon. Due to the marked difference of atomic weight and structure of the mentioned gases, krypton and xenon will have the highest adsorption affinity; V s

Although at the beginning of the cycle, all components of the air will be partially adsorbed, with advancing of the cycle, heavier and higher boiling point components will successively substitute the lighter components until the adsorbent capacity is exhausted. Therefore, in the temperature ranges indicated herein, at which the adsorbers are operated in the systemof this invention, the process of adsorption is suitably selective in adsorbing krypton, xenon and acetylene. I

Referring again to Fig. 1, after the exhaustion of the adsorbing capacity of the adsorbers, krypton, xenon and other gases, including hydrocarbons, 'are'desorbed from the silica gel by a small purge stream of a suitable gas or by the evacuation by a vacuum pump and a controlled increase of temperature.

If a purge gas is used for the desorbing treatment any suitable gas may be employed which is non-condensing in the second condenser at 2890 F. Gases such as nitrogen, helium or hydrogen may be introduced into the system from an independent source for use as a purge stream. If nitrogen is used for the purge stream, a portion of the nitrogen, which issues through conduit 21 from heat exchanger ltlmay'be diverted through line 32. This nitrogen purge-stream then may be passed through a recycling compresser 33 and a heater '34 and part of the stream passes through line 35 to the gas adsorber 14 which has previously been saturated with acetylene, xenon and krypton. Another portion or the purge stream passes through pipe 36' and-enters the liquid adsorbing chamber 16 which'has previously adsorbed acetylene, xenon'and krypton from the liquid oxygen erature in the, chambers 'to about +2 12 F.

A controlled desorption may be usedto provide'an opportunity to obtain selective "desorption at ditlerent temperature levels, i. e., fractions containing su'ccess'ively,

major partsof krypton, xenon and little of hydrocarbons, and thereafter major parts of hydrocarbons, including acetylene, and little krypton and xenon, to thus facilitate further separation of krypton and xenon from the hydrocarbon impurities. 7

The concentration ot'kr'ypton, 'xenon and hydrocarbohs 1n the purge stream is considerably higher than that inthe air because the desorption period is considerably shorter,

and the volume of the purge stream"much smaller than that'of air treated during the adsorption period. 7

The krypton enriched stream passes through condui't'37 to the condensing coil 17 which is maintained at :F. by means of the auxiliary, ethylene'refrig'eration unit i9 consisting of compressor 57 and condenser 58, and'whe'r'ein the acetylene and other hydrocarbons are solidified on the walls of the coils. .The purge stream continues through pipe 33 to the second condensing coil 18 which is maintained at 289 F. and wherein the krypton and xenon are deposited, in solid form, on the inside walls of the coils. Aftergdropping the acetylene, xenon and krypton, the purge gas stream passes through line 39 as lean purge stream of nitrogen in conduit 32 to be recycled through the desorbing and condensing apparatus. The recycling of the purge gas stream will decrease the loss of krypton and acetylene :vapors' remaining in the carrier stream in quantities'cOrreSpOnding to partial pressure of the purge and thus increase the yield of recovery. I

Another alternative arrangement for the desorption treatment is represented in Fig. 4 which utilizes evacuation by means of a vacuum pump for desorption of krypton and xenon from the adsorbers instead of recycling purged gas by a compressor 33 as shown in Fig. 1. Evacuation of adsorbers might prove to be preferable by doing away with a separate purge system. In the system shown in Fig. 4 non-condensable gases may be used by recycling them through the adsorbers to keep the vent losses of krypton and xenon, by saturated vapors at condensing temperature in effiuent from the condenser, low and thus increase the available recovery of rare gases.

More patricularly Fig. 4 represents a flow diagram of a vacuum desorption system which may be substituted for the desorption system illustrated in Fig. 1.

The gases from the gas adsorbers 130, 131 and from the liquid adsorbers 132 and 133 are desorbed by controlled increase of temperature by internal heating coils in the adsorbers or by non-condensable gases passed therethrough from the recycle heater 104. The desorbed gases are brought through the switch valve 135 from adsorber 136 and valve 140 from adsorber 133 to vacuum pump 72. The vacuum pump creates a partial vacuum on the adsorber which facilitates the desorption of the adsorbent and forces the desorbed gases through the cooler 73 at suitable condensation pressure. The gases are cooled down in cooler 73 and pass through valve 110 to the first condensing coil 87, and are cooled to approximately 150 F. by refrigeration unit 89 using a suitable low temperature refrigerant as for example ethylene. Acetylene precipitates in solid form on the walls of the condensing coil 37. Krypton, xenon and the non-condensable carrier gases all having boiling points below the temperature of the condenser 114, issue through line 108 and open valve 112 to second condenser 115. Krypton and xenon precipitate in solid form in coil 88 cooled to 289 F. by liquid oxygen conveniently supplied by line 170 from the bottom of a low pressure fractionating tower, as described in the arrangement shown in Fig. 1. Oxygen vapors evaporated in the condenser 115 by cooling of the gases and by the condensation of krypton and xenon in the coil 83 are returned as part of the cold oxygen product and may be routed through line 162 to a heat exchange unit similar to in Fig. 1.

The non-condensable carrier gases leaving coil 88 contain a small quantity of krypton and xenon vapors corresponding to vapor pressures of these gases at condensation temperature. In order to increase recovery yield, the stream of non-condensable carrier gases is recycled. The pressure is reduced by a throttle valve 111 and recycle gas is warmed up by heater 104. Warm recycle gases from heater 194 re-enter by conduit 185, gas adsorber 130 and by conduit 1% to liquid adsorber 133. The stream of noncondensable gases is again enriched in krypton, xenon and acetylene and is removed by the vacuum pump 72 through suction line 138, as described above. The pressure in the condenser system may be controlled by venting surplus non-condensable gases leaving the second condenser 115 by valve 125. Desorption pressure can be adjusted by the pressure reducing or throttle valve 111 for best selectivity of desorption.

The above described recirculation may be continued until all the krypton, xenon and acetylene gases are desorbed from the adsorbers and the adsorbent is completeiy regenerated.

It will be understood that the desorption and condensing circuit illustrated in Fig. 4 may be substituted for the similar circuit illustrated in Fig. l. The employment of either desorption circuit results in the acetylene being deposited in solid form in the first condenser coil, i. e., coil 17 of Fig. l or coil 87 of Fig. 4; and krypton and xenon being deposited in solid form in the second condenser coil, i. e., coil 18 of Fig. l or coil 88 of Fig. 4.

The dash lines in F 1 4 indicate conduit connections with the several parts of the oxygen recovery system aranged in a manner similar to that shown in Fig. 1.

Total heat losses of the desorption and the subsequent precipitation of acetylene, krypton and xenon in condensing coils can be reduced greatly in industrial installations by using countercurrent heat exchangers. However, the heat exchangers form no essential part of the system for the recovery of the rare gases, and, therefore, have not been included in the drawings.

In the second phase of the recovery of krypton, and xenon illustrated schematically inFi 2, the condensing coils 17, 18 are shut off periodically from the purge stream carrying acetylene, krypton, and xenon from the adsorbers, by closing valve 49 in conduit 37. Also valves 41, 42, are closed to isolate the condensing coils 17 and 18 from each other and to close the connections of coil 18 with the desorbing cycle of the apparatus. The coils 17 and 18 are thereupon suitably warmed; one effective means being to drain the ethylene and liquid oxygen from the coil containing chambers 44 and 45 and introducing a Warm stream of gas or liquid into the chambers through feed lines 46 and 47, as shown in Fig. 2.

In the final clearing of the condensers 17 and 18, which have been sufficiently warmed to re-evaporate or sublime the condensed substances contained therein, application of vacuum or a stream of a suitable carrier gas as nitrogen, CO2 or steam may be employed, and, in fact, one type of gas may be used for clearing one condenser and another carrier gas for clearing the other. For example, steam or CO2 may be used for carrying out the acetylene and other hydrocarbons in the higher temperature condenser 17 and nitrogen may be used to carry out the krypton and xenon contained in condenser 18.

In the apparatus as shown, it is contemplated that, as

the coils are warmed, a stream of nitrogen will be introduced into both coils passing through feed line 32, part of the stream being diverted through line 48 to coil 17 and part of the stream through line 49 to coil 18. During this phase of the operation, valves 50, 51 are opened to admit the stream of nitrogen into the respective coils. The hydrocarbons previously condensed in the coils are evaporated and are carried 011 by the carrier gas through conduit 52. During this phase of the operation, valve 53 is opened to permit the passage of the acetylenecarrying gas. The mixture in the carrier gas issuing through conduit 52 contains acetylene and other hydrocarbons and also includes a small amount of krypton and xenon. I

As the nitrogen stream passes into the coil 18 through line 49 the krypton and xenon which was previously condensed in the coil 18 is evaporated or sublirned and removed from the coils by the carrier gas through conduit 54, valve 55 being opened to permit the passage of the krypton and xenon bearing gas through line 54. This stream, in addition to the krypton and xenon, also contains a small amount of acetylene.

The krypton and xenon, sublimed from the condensing coils, will be present in the carrier gas in a much higher concentration than had existed previously in the air or in the oxygen bottoms from the low pressure fractionator used in conventional methods for recovery of krypton and it will also be in higher concentration than it was in the desorbing nitrogen purge stream.

The final fractionation of xenon and krypton from this carrier stream, their separation and purification, is considerably easier to accomplish than from mixtures produced by present methods. rom the krypton and xenon bearing stream the first step of purifying is to remove any trace of hydrocarbons which were not separated in the condensing apparatus, the removal may be eifected by catalytic burning in copper oxide furnaces and the carbon dioxide and water formed by the burning of the hydrocarbons in these furnaces can thereafter be removed by a caustic wash or other convenient means.

It is evident that the acetylene explosion hazards which previously have been the cause of considerable difiiculty in recovering krypton and xenon are practically eliminated by the fact that with the method of this invention, the acetylene, xenon and krypton mixture is handled in a nitrogen stream or in an insert carrier gas, instead of in an oxygen stream, as has been used in previous methods.

The final separation and purification of krypton and xenon from the nitrogen carrier stream may be effected by the conventional fractionation at low temperature and increased pressure. This method is well known and is particularly efiicient because there is a larger temperature differential between the respective boiling points of the xenon-krypton-nitrogen combination than between the respective boiling points of the combination of krypton-oxygen.

It will be appreciated that this invention, in addition to providing an efficient and effective method and apparatus for recovering xenon and krypton and for eliminating the explosion hazard during the recovery, also reduces the explosion hazard in the oxygen system by removing the acetylene impurities from the air before it is introduced into the high pressure air fractionator 11 and the low pressure oxygen rractionator 12. in the past, the hazard or explosion was present because of the dangerous accumulations of hydrocarbon impurities in the liquid bottoms of the fractionators during the recovery of oxygen.

During the operation of the xenon krypton recovery apparatus of this invention the main streams passing through the active adsorbers are never interrupted and they are continually being subjected to adsorption. This is possible because the desorption cycle is considerably shorter than the adsorption cycle and therefore the inactive adsorbers may be completely desorbed and then temporarily shut off from the condensers while the latter-are cleared during the adsorbing cycle of the active adsorber.

it will be appreciated that the advantages of the apparatus and method of this invention are found in the fact that the rerrigeration loss and power requirements are considerably less than those required by conventional methods because extraction of krypton and xenon by.

adsorption from the air stream does not require any additional refrigeration over a comparativety long period as do other methods which involve the continuous separation of krypton from oxygen bottoms by fractionation or large quantities or liquid oxygen with a low concentration of krypton, or xenon.

Furthermore, the equipment required for krypton and xenon recovery by low temperature adsorption is relatively simple and inexpensive. The two pairs of reversing adsorbers are simple and may be small vessels and the desorption .and krypton and xenon concentration equipment, operated intermittently, is handling small quantities of purge and carrier gases and reduces very considerably the required investment. 7

It will be appreciated that the temperatures and pressures indicated at which the various members of the apparatus are'operated are only illustrative and the apparatus may be effectively operated at other temperatures and pressures, providing the temperatures and pressures are in the range to effect the several physical changes in the materials which are being treated; particularly the air which initially is introduced into the adsorbing chambers should be sufficiently cooled, preferably below the boiling points of krypton and xenon and-of the hydrocarbon impurities but above the boiling points of oxygen and nitrogen in order to increase relative saturation of vapor of said rare gases and thus effect the adsorption of the krypton and the hydrocarbons.

The first condensing coils should be maintained below the melting point of the hydrocarbon impurities and particularly the acetylene, but above the melting point of krypton andxenon, and the second condensing coil should be maintained below the melting point of krypton and xenon to effect the selective condensation of the hydrocarbon impurities in the first condensing coil and the condensation of the krypton in the second condensing coil.

-I claim: 7

1'. A method of krypton and xenon recovery and purification, comprising, a stream of cooled compressed air passed into contact with silica gel to absorb the krypton and xenon and. hydrocarbon impurities from the air stream, desorbing the krypton and xenon and impurities from the silica gel by passing a Warm stream of nitrogen into contact with said silica gel and selectively condensing and freezing the hydrocarbon impurities and krypton and xenon from the nitrogen stream and thereafter separately evaporating :the krypton and xenon into a second gaseous carrier stream. I

' 2. in a krypton and xenon recovery system wherein krypton and xenon, together with hydrocarbon impurities are adsorbed at low temperatures from a stream of cool compressed air and wherein the adsorbed krypton and xenon andhydocarbon impurities are thereafterdesorbed into a warm carrier stream of nitrogen; a method of removing the krypton and xenon from; the stream of nitrogen, comprising, passing the nitrogen stream through a pair of condensing coils maintained at selected temperatures, the first coil being maintained at a temperature below the melting point of the hydrocarbon impurities but above the boiling point of kryptonand xenon to thereby condense and freeze out the impurities and thereafter passing the krypton and xenon carrying nitrogen stream through the second condensing coilfmaintai'ned at a temperature below the melting pointof krypton to condense'andfreeze out the krypton and xenon.

3. 1n the method of claim 2 recovering xenon and krypton from the second coil by passing a warm gaseous stream through the coil to sublime the krypton into said stream.

4. A method of recovering krypton and xenon from air and separating them from the hydrocarbon impurities in the air, comprising, passing a stream of air cooled below the boiling point of krypton into contact with an adsorbent material to thereby adsorb the krypton and xenon and the hydrocarbon impurities in the air stream, desorbing xenon and krypton into a stream of nitrogen which has been warmed above the desorption point of krypton, subsequently cooling and condensing and freezing the hydrocarbon impurities from the nitrogen stream and thereafter condensing and freezing the krypton and xenon from the nitrogen stream.

5. In an apparatus for krypton and xenon recovery and purification, at least one pair of adsorbers and at least one pair of condensers, means for introducing cool compressed air into the adsorbers alternately and means for introducing a warm stream of nitrogen into sai adsorbers alternately for desorbing the krypton and xenon which had been adsorbed in said adsorbers, and means for conducting the krypton and xenon enriched stream of nitrogen through the two condensers successively, cooling means associated with the first condenser for cooling below the freezing point of the impurities in the nitrogen stream and means for cooling the second condenser below the freezing point of the krypton and xenon carried in the nitrogen stream.

6. In the apparatus of claim 5 wherein means are provided for periodically warming the first and second condensers and evaporating the condensate therein and means for passing separate carrier streams through the respective condensers for removing the respective condensates.

7. A system for recovering krypton and xenon from air and removing the impurities from the krypton and xenon, said system comprising, in combination, an adsorbing circuit comprising'in recited sequence means for receiving dried compressed air, meahsfor holding a mass of adsorbent material adapted :to adsorb krypton and xenon in the path of the flow of the cooled air, a desorbing circuit, including, in recited sequence, means for periodically diverting a stream of warm nitrogen through the means for holding the adsorbent material for desorbing the krypton and xenon contained therein, means for feeding the krypton and xenon enriched nitrogen stream into contact with the condensing means adapted to selectively condense the krypton and xenon from the nitrogen stream.

8. In an oxygen recovery system comprising, a cooling means, a high pressure at fractionator, a low pressure oxygen fractionator, an auxiliary krypton and xenon;

recovering and purifying system comprising, in cornbina tion, an adsorbing circuit and a desorbing circuit, and means for periodically and alte'rnatelyoperating said circuits, said adsorbing circuit comprising, in recited sequence, means for feeding dried compressed air through the cooling means of the oxygen system, means for hold-.

ing a mass of adsorbing material, adapted to adsorb krypton and xenon-from the cooled air, in the path of the fiow of said air, said desorbing circuit comprising means for heating and compressing nitrogen, and means for delivering said nitrogen into contact with the krypton and xenon saturated mass of adsorbent material, said nitrogen being adapted to dcsorb the krypton and xenon from the adsorbent material, and means for directing the iiow of the krypton and xenon enriched nitrogen stream to successive condensing means .rnaintained at temperatures adapted to selectively condense the hydrocarbon impurities and the krypton from the nitrogen stream.

9.111 an apparatus for recovering and purifying krypton and xenon, the combination comprising an adsorbing circuit, a desorbing-and condensing circuit and an evaporating circuit, said adsorbing circuit comprising, in sequence, means for receiving dried compressed air, means for cooling the air, means for holding a mass of adsorbent material :in the path of flow of the thus cooled air, said adsorbent material being adapted to.

adsorb *krypton and xenon and certain hydrocarbon impurities from th'e cooledair a'nl, na'ean's for delivering the krypton and xenon and hydrocarbons from air from the adsorbent holding means; said desorbing circuit comprising, in recited sequence, means for diverting a stream of purge gas, means for heating and compressing the purpe gas and means for delivering said heated and compressed purge gas into the said means for holding the mass of adsorbing material, said purge stream being adapted to desorb the krypton, xenon and the hydrocarbon impurities from the adsorbent material, and at least two condensing means having cooling means associated therewith adapted to maintain the condensing means at selected temperatures and means for directing the krypton and xenon and hydrocarbon enriched purge gas stream through said condensing means successively to effect selective condensation of the hydrocarbons and the krypton and xenon, said evaporating circuit comprising, in recited sequence, means for periodically warming the said condensing means, means for directing separate carrier streams through said condensing means, said carrier streams being adapted to evaporate and carry off the hydrocarbon condensate and the krypton and xenon condensate of the respective condensing means, and means for periodically and sequentially directing the respective gaseous fluids through the successive circuits.

10. A method of krypton and xenon recovery and purification, comprising, passing a stream of cool compressed air into contact with silica gel to adsorb the krypton, xenon, and hydrocarbon impurities from the air stream, desorbing the krypton and xenon and impurities from the silica gel by repeatedly recycling a warm stream of purge gas into contact with the silica gel and passing the stream through at least two condensing and freezing areas for selectively and separately condensing and freezing the hydrocarbon irn purities and krypton and xenon from the purge stream temporarily disconnecting the condensing and freezing areas from the stream of purge gas and thereafter separately evaporating the krypton and xenon into a second gaseous carrier stream.

11. In a system of krypton and xenon recovery and purification wherein krypton and xenon and hydrocarbon impurities are adsorbed from cooled compressed air passed into contact with an adsorbent material, the method of desorbing the krypton and xenon and hydrocarbons from the adsorbent material and thereafter selectively and separately condensing and freezing the krypton and xenon and hydrocarbons comprising repeatedly recycling and warming a stream of purge gas and passing it successively into desorbing contact with the adsorbent material and thereafter passing the stream through at least two condensing and freezing areas for selectively and separately condensing and freezing the hydrocarbons and krypton and xenon from the purge stream.

12. In a process for producing oxygen from air in which a continuous stream of cold air.under pressure flows to fractionating equipment for separation into its constituents, the process of separating krypton and xenon from said cold air stream without interrupting its continuous flow which comprises alternately introducing a selective adsorbent into the cold air stream, and selectively desorbing hydrocarbon impurities and krypton and xenon from the inactive adsorbent while it is out of contact with the cold air stream.

13. In a krypton and xenon recovery system, where krypton and xenon together with hydrocarbon impurities are adsorbed at low temperatures from a stream of cool compressed air and wherein the adsorbed krypton and xenon and hydrocarbon impurities are thereafter desorbed into a warm carrier stream of inert gases, comprising, passing the carrier stream through a pair of condenser coils maintained at selected temperatures, the first coil being maintained at a temperature below the melting point of the hydrocarbon impurities but above the boiling point of krypton and xenon to thereby condense and freeze out the impurities and thereafter passing the krypton and xenon carrying stream through the second condensing coil maintained at a temperature below the melting point of krypton to condense and freeze out the krypton and xenon.

14. The method described in claim 13 wherein the carrier stream is helium.

15. The method described in claim 13 wherein the carrier stream is hydrogen.

16. A method for recovering krypton and xenon from air containing hydrocarbon impurities, comprising, cooling and compressing a stream of air and passing it into contact with an adsorbent material thereby adsorbing the krypton and xenon and the hydrocarbon impurities from the air stream, desorbing the krypton and xenon from the adsorbent material by a purge stream of nitrogen passing the stream through successive coolers at predetermined controlled temperatures, thereby selectively freezing out the krypton and xenon from the purge stream and thereafter independently recovering the hydrocarbon impurities and the krypton and xenon.

17. In a process for producing oxygen from air in which a continuous stream of cold air under pressure flows to fractionating equipment for separation into its constituents, the process of separating krypton and xenon from said cold air stream Without interrupting its continuous flow which comprises alternately introducing a selective adsorbent into the cold air stream, and selectively desorbing hydrocarbon impurities and krypton and xenon from the inactive adsorbent while it is out of contact with the cold air stream by warming the adsorbent first to a low temperature to drive off the krypton and xenon and then increasing the temperature of the adsorbent to drive off the hydrocarbon impurities.

18. In a process for producing oxygen from air including compressing and cooling the air and fractionating liquid air under pressure, the method of recovering krypton and xenon, comprising first adsorbing the bulk of the krypton, xenon and hydrocarbon impurities from the cool air stream in the gas phase before the pressure fractionation takes place and finally adsorbing the remaining krypton, xenon and hydrocarbon impurities in the liquid phase, desorbing krypton, xenon and hydrocarbon impurities from the two adsorption stages and selectively recovering the hydrocarbon impurities, and the krypton and xenon.

19. In a process for producing oxygen from air including compressing and cooling the air and fractionating the liquid air under pressure, the method of recovering krypton and xenon, comprising first adsorbing the bulk of the krypton, xenon and hydrocarbon impurities from the cool air stream in the gas phase before the pressure fractionation takes place, adsorbing the remaining krypton, xenon and hydrocarbon impurities in the liquid phase, desorbing the krypton, xenon and hydrocarbon impurities by means of a warm purge gas and recovering the krypton and xenon independently by first cooling the purge gas to selectively freeze out the hydrocarbon impurities.

20. In a process for producing oxygen from air including the compressing and cooling of the air and the fractionation of liquid air under pressure, the method of recovering krypton and xenon, comprising first the adsorption of the bulk of the krypton, xenon and hydrocarbon impurities from the cool air stream in the gas phase before the pressure fractionation takes place and finally the adsorption of the remaining krypton and xenon in the liquid phase, desorbing the krypton, xenon and hydrocarbon impurities from the adsorption stages by a purge gas and selectively freezing out of said purge stream krypton and xenon, and the hydrocarbon impurities in separate condensers operated at different temperatures, temporarily disconnecting the condensers and recovering the krypton and xenon by means of an independent recovery gas. i

References Cited in the file of this patent UNITED STATES PATENTS 879,129 Dewar Feb. 11, 1908 1,670,014 Blaringhem May 15, 1928 1,682,588 Wietzel et a]. Aug. 28, 1929 1,772,202 Blaringhem Aug. 5, 1930 1,891,125 Gessel Dec. 13, 1932 1,948,779 Abbott et al. Feb. 27, 1934 2,060,940 Kahle Nov. 17, 1936 2,093,805 De Baufre Sept. 21, 1937 2,374,091 Garrison Apr. 17, 1945 2,584,381 Dodge Feb. 5, 1952 

1. A METHOD OF KRYPTON AND XENON RECOVERY AND PURIFICATION, COMPRISING, A STREAM OF COOLED COMPRESSED AIR PASSED INTO CONTACT WITH SILICA GEL TO ABSORB THE KRYPTON AND XENON AND HYDROCARBON IMPURITIES FROM THE AIR STREAM, DESORBING THE KRYPTON AND XENON AND IMPURITIES FROM THE SILICA GEL BY PASSING A WARM STREAM OF NITROGEN INTO CONTACT WITH SAID SILICA GEL AND SELECTIVELY CONDENSING 